Brendan Schaub is a legend killer, defeating K-1 Grand Prix 2012 and PRIDE Open Weight 2006 Tournament Champ Mirko Cro Cop and also defeating Gabriel Gonzaga, a UFC legend by proving that the UFC Heavyweights were the best when he annihilated Prime Mirko Cro Cop who was on a killing streak. He beat both guys with the greatest of ease.
We all know he would've beaten Big Nog if the ref didn't stop it early, he was clearly playing possum to lure Nog into a ground war and submit him in zombie mode like Mir did but the ref stopped it early. if they rematched and also there was no ref conspiracy (let's be honest, Big Nog's team might have paid the ref to stop the match early) to stop the Legend Killer Brendan Schaub, he would join the small list of people that have submitted Big Nog in MMA: Fabricio Werdum and Frank Mir. or alternatively he could join the equally small club of people that have finished Big Nog by TKO: Frank Mir and Cain Velasquez.
as for Ben Rothwell, Schaub would destroy him in a rematch too. Brendan Schaub was acting cocky and thought he could outstrike the legendary striker Ben Rothwell (who recently defeated MMA legend Brandon Vera, a man whom many thought was capable of holding the HW and LHW UFC titles at once) to prove a point, but we know how that turned out. nowadays, Schaub wouldn't try that and would get it down to the ground ASAP and choke him out with his legendary BJJ skills. Schaub wins that fight 99/100 times and we all know it, I don't think Ben Rothwell wants a rematch tbh. same logic applies to Roy Nelson.
he most definitely can defeat current champ Cain Velasquez and top contender Junior dos Santos, he just needs to get them in his world by taking it to the mat. (the BJJ world, where he can effectively shut their games down, just like how he destroyed and annihilated Cyborg at Metamoris)